Mass polymerization of styrene at 285u deg. c.



Patented Apr. 22, 1952 MASS POLYMERIZATIONOF STYRENE AT 285 C.

Harold F. Park, East Longmeadow, Masa, as-

signor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application November 19, 1949,

1 Claim. 1

This invention relates to a process for preparing polystyrene. More particularly, the invention relates to a process for the mass polymerization of styrene at elevated temperatures to obtain polymers suitable for molding purposes.

Previous to this invention the polymerization of styrene to obtain polymers suitable for molding compositions has been carried out at temperatures below 100 C. in the presence of catalysts such as benzoyl peroxide, ditertiary butyl peroxide, tertiary butyl hydroperoxide and similar well known polymerization catalysts. At the temperatures usually used for mass polymerization, the duration of the polymerization process was generally from 18-30 hours and the resulting polymer frequently contained more than 3% of methanol-soluble materials which were harmful to the molding powders produced therefrom.

It also has been known that above 100 C., polystyrene polymerizes to polymers having a relatively low degree of polymerization. These low polymers are brittle and cannot be molded into useful articles.

An object of this invention is to provide a :new process for polymerizing styrene.

tion of styrene, at temperatures between 100 C.

and 400 C. in contact with an organic compound which is thermally unstable at temperatures between 100 C. and 400 C. and which dissociates into radicals containing one unpaired electron and an ethylenically unsaturated group.

; Examples of the catalysts of this invention are cinnamoyl peroxide, p,p'-divinyl benzoyl peroxide, acrylyl peroxide, methacrylyl peroxide.

crotonyl peroxide, etc. They are characterized by the presence of two ethylenically unsaturated groups which upon dissociation of the molecule are attached to separate radicals.

The following examples are given in illustra- Serial No. 128,473

tion and are not intended as limitations on the scope of this invention. Where parts are mentioned, they are parts by weight.

. Example I A mixture of parts of pure monomeric styrene and 1.0 part of cinnamoyl peroxide was placed in a stainless steel pipe capped at one end. The mixture was boiled for about 15 minutes at atmospheric pressure to remove dissolved oxygen. The mixture was then cooled in a nitrogen atmosphere and the other end of the stainless; steel pipe was firmly capped so that both ends of the pipe were sealed. This sealed pipe was then placed in a molten tin bath at a temperature of 370 C. and kept in said bath at a temperature of 370 C. for 5 minutes. The pipe was then removed from the bath, cooled to room temperature and opened. A solid transparent rod of polystyrene was obtained which was thermoplastic and could be easily molded by the con.- ventional injection or compression molding processes.

When the process of Example I was repeated, using no catalyst or benzoyl peroxide as a catalyst, the product was a friable weak polymer which could not be molded by the conventional molding methods.

It is sometimes advantageous to conduct the process of this invention in the presence of a reducing agent. Many such materials are known and have been used in polymerization reactions. The preferred reducing materials for this invention are metallic salts of alpha,beta-unsaturated acids since this class of compounds does not produce a color or haze in the polymer produced. Examples of such compounds are copper acrylate, nickel maleate, lead methacrylate, etc. Other reducing agents which may be used are quinones, organic sulfinates, aldehydes, amines, alcohols, thio-acids, mercaptans, ascorbic acid, and sulfur dioxide.

Erample II 100 partsof styrene were placed in a heavy, walled pyrex tube and 0.1 part of p,p'-divinyl benzoyl peroxide and .0001 part of copper acrylate were dissolved in the monomer. Dissolved and occluded oxygen were removed from the styrene by boiling thestyrene under about '5 min. of mercury pressure. The tube was then of 370 C. for minutes.

sealed without releasing the vacuum and the sealed tube was immersed in a molten Arochlor bath at 270 C'. The tube was kept in the 270 C. bath for about minutes and it was then cooled and broken to obtain a crystal-clear rod of polystyrene which had excellent strength, physical properties and could be easily molded by the conventional methods.

When Example II was repeated, using the same amount of copper acrylate, but no p,p'-divinyl benzoyl peroxide a friable, non-moldable powder product was obtained.

Example III 100 parts of a solution of polystyrene in styrene monomer, in which the styrene monomer constituted 68% by weight of the total, were mixed with 0.015 part of crotonyl peroxide and the mixture was passed continuously under a pressure of about 250 p. s. i. through a nickel pipe heated to about 285 C. The cross-section of the pipe, the length of the heated section of the pipe, and the pressure were so regulated that the polystyrene solution remained in the heated portion of the pipe for about 7 minutes. During the 7 minutes in the heated zone, the monomer polymerized and the continuous pressure forced it from the heated zone through the cooler end of the pipe. The polystyrene thus obtained could be molded and the articles made therefrom had excellent color, clarity and physical properties. The monomeric styrene content of the polymer was substantially zero.

Example IV A solution of polystyrene in styrene monomer, in which. the styrene monomer constituted 72% by Weight, said solution containing 0.09 part of acrylyl peroxide was forced into a standard screw extruder under a pressure of 250 p. s. i. The barrel of the extruder was heated to 285 C. The polystyrene solution was then extruded at 285' C.

'at' a rate of approximately 450 pounds per hour.

Eznample V A-mixture of 70 parts of styrene, 30 parts of alpha-methyl styrene and 0.1 part of methacrylyl peroxide was placed in a stainless steel pipe capped at one end. The mixture was boiled for about 15 minutes at atmospheric pressure to remove dissolved oxygen. The mixture was then cooled in a nitrogen atmosphere and the other end of the stainless steel pipe was firmly capped so that both ends of the pipe were sealed. The sealed pipe was then placed in a molten tin bath at 370 C. and kept in said bath at a temperature The pipe was then removed from the bath, cooled to room temperature and opened. A solid transparent rod of a copolymer of styrene and alpha-methyl styrene was obtained which could be easily molded by conventional means.

The process of. this invention may be carried out at temperatures between 100 C. and 400 C. It is preferable to carry out the invention in the absence of oxygen and other materials which are known to cause polymerization at temperatures below 100 C. The length of the polymerization cycle determines to some extent. the molecular weight of the polymer produced. A short cycle from 10-15 minutes at 400 C. can be used to obtain polymers of relatively low molecular weight and a cycle as long as 30 minutes at C. may be used to produce polymers of considerably higher molecular weight but still moldable in nature. In any event, the polymerization cycle need be no longer than 30 minutes compared with 18-30 hours necessary by previous processes.

The amount of catalyst used may vary between 0.01 part and 5 parts per 100 parts of styrene. At the lower part of the range, polymerization is slow unless the higher temperature range is used, and the molecular weight of the polymer is relatively high. At from 3-5 parts, polymerization is quite rapid even at 100 C. and the product is so low in molecular weight that it approaches the lower limit of moldability. In order to obtain the most accurate control of the reaction rate and to produce: an optimum range or moldable polymers, the amount of catalyst is preferably restricted to from 0.01 to 1.0 part per 100 parts of styrene.

The reducing agent which is optional serves the purpose of activating the catalysts and increasing the reaction rate. It has little or no eifect on the molecular weight of the polymer nor on the physical'properties thereof. It should be used in quantities ranging from 0.1" to 15 parts per million parts of styrene.

Various methods and apparatus may be used for polymerizing the styrene under the conditions of this invention. For example, it may be polymerized in sealed glass tubes or sealed metal tubes. The monomer or solution of polymer in the monomer may be forced through a heated metal tube or a heated glass tube, or a solution of a partial polymer in the monomer may be forced through a screw extruder, etc. The main precaution to be taken in any of the apparatus is the substantial exclusion of oxygen from the monomer.

In. some cases, it may be desirable to polymerize a solution of a polymer of styrene in monomeric styrene. This method results in the use of a viscous liquid as a raw material, such a liquid being more easily handled in continuous operations. In such solutions the monomer'preferably constitutes 60-80 weight percent of the solution. 1

The process of this invention is applicable to styrene and mixtures of styrene with vinylidene compounds in which mixtures the styrene constitutes the major proportion by weight. Among the compounds. which may be polymerized with styrene in the process of this invention are alpha-alkyl styrenes such as alpha-methyl styrene; chlorostyrenes such as p-chlorostyrene, 2,5-dichlorostyrene, divinyl benzene, vinyl pyridine, vinyl quinolines; vinyl esters such as vinyl acetate, vin l but-yrate; acrylic and alpha-substituted acrylic acids and the esters, nitriles and amides thereof such as methyl acrylate, ethyl acrylate, acrylonitrile, acrylamide, methyl methacrylate, butyl methacrylate, methyl phenacrylate, methacrylonitrile, methacrylamide, etc.; alphabets.-ethylenically' unsaturated dicarboxylic acids and anhydrides and the esters and amides and nitriles thereof such as maleic acid,

maleic anhydride, fumaric acid, fumaronitrile,

etc; dienes such as butadiene, isoprene, piperylene, etc.; vinyl halides, vinyl chloride, vinylidene chloride, etc.

This invention provides a simple process for preparing moldable polymers of styrene and co- 7 polymers of styrene, in which the styrene is a predominant part, by polymerizing the styrene monomer or monomer mixtures in a matter of minutes rather than a matter of hours or days as has been previously necessary. The process has the further advantage that the products contain substantially no volatile material, are easily moldable, and do not deteriorate upon ageing.

It is obvious that many variations may be made in the products and processes of this invention without departing from the spirit and scope thereof as defined in the appended claim.

What is claimed is:

A mass polymerization process which cornprises polymerizing styrene in contact with acrylyl peroxide at 285 C. in from 5 to 30 minutes.

' HAROLD F. PARK.

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